Semiconductor laser

ABSTRACT

In a semiconductor laser, at least one temperature sensor is disposed directly on or integrated in a semiconductor laser chip for measuring an operating temperature. Precisely and/or locally solved measurement of the operating temperature of the laser are possible. One or more temperature sensors may be placed and fastened directly onto the laser chip or in a hole of the laser chip by welding, especially with Nd-YAG-laser light or light with similar characteristics. Fine equalization of temperature may be carried out, for example, by Peltier elements, components of the Peltier elements being mounted directly onto the laser chip. A cascaded arrangement of thermoelements and Peltier elements on a laser chip is also provided for.

FIELD OF THE INVENTION

The present invention relates to a semiconductor laser in general, and,particular, to a semiconductor laser including a semiconductor laserchip and at least one temperature sensor secured directly to orintegrated in the semiconductor laser chip.

RELATED TECHNOLOGY

Semiconductor lasers are generally known, as proceeds, for example, fromthe publication by H. Richter, TelekomVision 7/93, Chips mitZukunftspotential” [Chips with Future Potential], interim results of theTelekom Research Project OEIC, TelekomVision 7/93, pp. 41 through 47,which is hereby incorporated by reference herein.

The application of such a laser is described in detail in thepublication by K. H. Park, “Fabrication and Transmission Experiments ofDistributed Feedback Lasers Modules for 2.5 Gb/s Optical TransmissionSystems” published in Optical and Quantum Electronics 27 (1995),547-552. To further enhance capacity, optical carrier frequencytechnologies, also referred to as wavelength division multiplex systems,are increasingly being used. The output wavelength of the semiconductorlasers used in these systems must be able to be adjusted and correctedwithin a very narrow range. Manipulated variables used for this purposeinclude the externally adjusted temperature of the laser carrier, andthe laser's pumping power.

At a constant pumping power, an incorrect determination of thetemperature of the laser chip leads to deviations in the outputwavelengths, particularly when it is necessary to change the pumpingpower for operational reasons. The reasons for a change in pumping powercan be unplanned, such as the effects of ageing on the laser, or alsoplanned, such as changing the laser's output power in response to achange in path attenuation, or subsequent to a reconfiguration inswitched networks (routing, equivalent line circuit).

While in telecommunications lasers the emphasis is on a monomodecharacteristic and a small line width, as well as a rapid modulability,for purposes such as material processing, it is important that thesemiconductor laser have a high power output. In comparison totelecommunications lasers, high-performance lasers are often very long(up to 2 mm). Unavoidable irregularities due to manufacturing, along theactive laser zone, lead to local temperature peaks, particularly inoperations entailing the highest power outputs. Such irregulartemperature distribution results in a diminished output power and, inthe extreme case, to irreversible degradation of the laser.

In known methods heretofore, a laser's temperature is only measured atone location, namely at its laser carrier being used as a heat sink.When measuring the temperature, errors can occur due to the heattransfer resistance between the laser chip and the heat sink, and alsodue to the finite thermal conductivity of the laser chip material; inaddition to this such errors are caused by other heat sources producedby the bulk resistances in the pumping current's circuit path. Besidesthe steady-state temperature measuring errors, large time constants alsoresult, which adversely affect temperature control. In known methodsheretofore, irregularities in the temperature characteristic were notrecorded at all in the case of high-performance lasers. German PatentNo. DE 19 546 443 and European Patent No. EP 0 779 526, which are herebyincorporated by reference herein, describe an optical and/orelectro-optical connection, and a method for manufacturing such aconnection for two optical and/or electro-optical components. FIG. 7 ofEuropean Patent No. EP 0 779 526, in particular, shows how apump-current lead wire is secured in a semiconductor laser, and providesdetails of the same in the corresponding description. It also describeshow a hole can be bored into a laser chip using laser welding light.

Other laser chips or semiconductor laser modules are fundamentallydescribed in German Patent No. DE 42 32 326 and in German Patent No. DE42 32 327.

As noted above, it is customary for the temperature of a laser to bemeasured at only one location, namely at its laser carrier being used asa heat sink.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an arrangement of atemperature sensor or of a plurality of temperature sensors, which willenable a more precise and/or locally resolved measurement of theoperating temperature, it also being possible to implement a precisetemperature adjustment with substantial accuracy and/or localselectivity.

The present invention provides a semiconductor laser including asemiconductor laser chip and at least one temperature sensor disposeddirectly on or integrated in the semiconductor laser chip for measuringan operating temperature. A very high precision, not attainable in knownmethods heretofore, is achieved by securing one or a plurality oftemperature sensors directly onto the laser chip, and in intimateconnection with the same, in a welding operation using Nd-YAG laserlight or light having similar properties. The fine temperatureadjustment is advantageously carried out using Peltier elements, thecomponents of the Peltier elements being applied directly to the laserchip using Nd-YAG laser light. In accordance with the present invention,the wavelength of the laser chip is measured and, when necessary, thewavelength of the laser chip is also adjusted, the telecommunicationslasers having one measuring point per active laser zone, and thehigh-performance lasers having a plurality of measuring points per laserchip along the active laser zone.

Other advantages, features, and possible applications of the presentinvention are revealed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention shall be elucidated with reference to thedrawings, in which:

FIG. 1 a schematic diagram of a semiconductor laser chip in accordancewith the related art;

FIG. 2 a schematic diagram of an arrangement and mounting of a knownsensor on the laser chip;

FIG. 3 a schematic diagram of a sensor encapsulated in glass;

FIG. 4 a schematic diagram of a semiconductor laser chip having a holebored by laser welding light;

FIG. 5a a schematic diagram of an arrangement having a bulk resistor asa sensor;

FIG. 5b a schematic diagram of an arrangement having a symmetricalsensor;

FIG. 6 a schematic diagram of a representation of the bulk resistance inparallel to the pumping current circuit;

FIG. 7 a schematic diagram of an arrangement for measuring thetemperature of individual lasers using bulk-resistance sensors;

FIG. 8 a schematic diagram of an arrangement for measuring temperatureirregularity using bulk-resistance sensors;

FIG. 9 a schematic diagram of a thermoelement mounted on a laser chip;

FIG. 10 a schematic diagram of a thermoelement having only oneadditional wire;

FIG. 11 a schematic diagram of an arrangement for regulating temperatureusing a thermoelement and a Peltier element;

FIG. 12 a schematic diagram of a cascaded arrangement of thermoelementson a laser chip; and

FIG. 13 a schematic diagram of an arrangement for locally selectivetemperature regulation.

DETAILED DESCRIPTION

FIG. 1 shows the design of a known laser chip, as described, forexample, in H. Richter, “Chips mit Zukunftspotential” [Chips with FuturePotential], discussed above. Up until now, a laser's temperature hastypically been measured at one location, namely at its laser carrierthat is used as a heat sink. In this context, a temperature sensor 1,together with its lead wires 2 and 3, is mounted on heat sink 6.Semiconductor laser chip 4, also referred to simply as laser chip,receives a pumping current at its active laser zone 5 via wires 7 and 8that supply the pumping current. As already described at the outset, anarrangement of this kind has the following disadvantages: the differencebetween the temperature of semiconductor laser chip 4, which is alsodeterminative for the output wavelength of the laser, and the externallyadjusted temperature of heat sink 6, is not recorded. The temperaturedifference is caused by the heat transfer resistances between laser chip4 and the laser carrier or heat sink 6, as well as by the finite thermalconductivity of the laser chip material. The bulk resistances in thepumping current circuit are also a source of heat. The result is notonly steady-state measuring errors of temperature, but large timeconstants as well, which have an adverse effect on a temperaturecontrol.

FIG. 2 illustrates how an already known temperature sensor 1 can beapplied by welding using laser light to laser chip 4. The remainingdesign of the arrangement according to FIG. 2 corresponds to that ofFIG. 1. Melting points 10 formed using this welding method securetemperature sensor 1 to laser chip 4, as shown in FIG. 3.

According to the specific requirements, it can be necessary and/or alsoadvantageous to encapsulate temperature sensor 1, before applying it tolaser chip 4, in a thermally conductive, easily weldable material 9, forexample glass, as shown in FIG. 3. The remaining design correspondsagain to that already described previously, however heat sink 6 ofsemiconductor laser 4 is not shown, since the intention here is tomerely show the arrangement of an encapsulated temperature sensor 1.

FIG. 4 depicts such a temperature sensor 1 in a predrilled hole. Shownhere, again, is laser chip 4 having wire 8 for supplying pumpingcurrent, as well as wires 2 and 3 for suppling measuring current totemperature sensor 1. Also shown, are wires 2 and 3 for supplyingmeasuring current to temperature sensor 1.

To produce the hole for temperature sensor 1 in laser chip 4, laserlight radiation can likewise be used, as described in German Patent No.DE 19 546 443.

At this point, it should be remarked that the described method forarranging one or a plurality of temperature sensors, as well as the finetemperature adjustment characterized by high precision and/or localselectivity with respect to temperature is easily applicable to laserchips of thermally isotropic material.

The arrangements in accordance with FIGS. 5a, 5 b and 6 enable thetemperature dependency of bulk resistor 11 itself to be measured. Theresistor is apparent between the two melting points 10, where the twowires 2 and 3 for supplying measuring current are mounted by welding oranother method, for example bonding. Also shown are lead wires 2 and 3for the measuring current and lead wire 8 for the pumping current.

FIG. 5b shows an arrangement having symmetrical sensors, individuallaser 5 being configured symmetrically between melting points 10 inlaser chip 4. Here, bulk resistor 11 is again disposed between the twomeasuring points 10.

FIG. 6 illustrates that bulk resistor 11 is arranged in parallel to thepumping current circuit, here again, heat sink 6 being connected tolaser chip 4 by melting points 18 formed during welding. Heat sink 6 isconnected by a wire 7 for supplying the pumping current, and individuallaser 5 is likewise connected by a wire 8 for supplying the pumpingcurrent. Wire 3 is connected to melting point 10, to be able to supplythe necessary measuring current.

The need is eliminated here for second melting point 10 for wire 2;instead, wire 7 or wire 8 can be jointly used.

Measuring the temperature of individual lasers 5 having bulk-resistancesensors is illustrated in FIG. 7. The individual bulk resistors 11 aredisposed between melting points 10 of individual lasers 5, which arelocated on or in a laser chip 4. This demonstrates that when a pluralityof individual lasers 5 are configured on one laser chip 4, thetemperature of each individual laser 5 can be measured. As a result, itis possible to adjust the output wavelengths of these individual lasers5 during operation, by way of their pumping currents, without explicitlymeasuring their wavelength.

A similar technology (FIG. 8) makes it possible, when working withhigh-performance lasers, to measure the temperature distribution alongan active-laser zone of an individual laser 5 on or in laser chip 4.

Particular advantages are derived when temperature sensor 1 is athermoelement. It is then not only possible to secure a previouslyfabricated thermoelement using laser-light welding, directly onto themeasuring object, in close thermal contact with the same, as alreadydescribed, but it is also possible, in one work step, to join the twoindividual wires required for the thermoelement, using laser-lightwelding, to form one thermoelement, and to secure it to the measuringobject.

As is evident in FIG. 9 from the arrangement of a thermoelement on alaser chip 4, each thermoelement, shown here as measuring point 12, nowhas one measuring lead wire 2 and one measuring lead wire 3, each ofdifferent material.

Before joining wires 2 and 3 on laser chip 4, it is particularlyadvantageous to vapor-deposit a contact surface 21 on semiconductorlaser 4, or to apply it in some other suitable way, this surface 21either being made of the material of wire 2 or of the material of wire 3(FIG. 9).

At the second place where wires 2 and 3 are united, a secondthermoelement 13 is formed. At point 14, a voltage that is dependentupon the temperature difference between points 12 and 13 can then betapped off; in this context, the measuring instrument at point 14 issurrounded by wires of the same material. Of course, wires 2 and 3 canalso be partially or completely designed as printed conductors that arepermanently connected to a chip (e.g., to laser chip 4).Temperature-reference point 13 can be on chip 4 itself, on heat sink 6of semiconductor laser 4, or even on the housing surrounding the entirearrangement, in accordance with FIG. 1.

FIG. 10 shows a design variant that makes do with only one additionalwire 3, in which the otherwise necessary wire 2 is the pumping-currentlead wire 8, made, for example, of gold or copper. The other wire 3 forthermoelement 12 is made, for example, of Konstantan.

A further advantage is derived in a reversed operation by using athermoelement in accordance with FIG. 11 as a Peltier element having acurrent source 17. Similarly to the measuring arrangement according toFIG. 9, here as well, wires 19 and 20 between points 15 and 16 are madeof different materials. Depending on the direction of the current fromsource 17, the heat can be transferred from point 15 to point 16 (mainapplication case: semiconductor laser 4 is cooled) or from point 16 topoint 15 (semiconductor laser 4 is additionally heated).

The Peltier element formed from wires 19 and 20 between points 15 and 16is fabricated using the same technology as thermoelement pair 2, 3, 12,13, described in FIG. 9.

Using a thermoelement pair functioning as a temperature sensor, inaccordance with FIG. 9, and a Peltier element 15, 16, 19, 20 operated asa temperature setter, one can precisely adjust the temperature of point15. To reduce control errors, point 15 should be close to point 12. Thecontroller (not shown) then controls current source 17 as a function ofmeasuring voltage 14 of thermoelement pair 12 and 13, measuring point 13being an external reference point. In this control, it is beneficial forreference point 13 and thermal reference point 16 (in an embodiment, aheat sink) of the Peltier element to have the same temperature. Thisreference location 13 or 16 can be a point outside of the laser housing(for measurement as compared to ambient temperature). However, it isalso possible for the reference location to be placed on heat sink 6 ofsemiconductor laser 4 (for measurement of the differential temperaturewith respect to heat sink 6 of semiconductor laser 4, if indicated, withheat dissipation likewise to heat sink 6 of semiconductor laser 4).

If semiconductor laser 4 is a telecommunications laser, then its outputwavelength can be very finely tuned.

For very long lasers 4 (for example, high-performance lasers), it isalso possible—as shown in FIG. 12—to configure both thermoelementelement pairs 12 and 13, as well as Peltier elements 15 and 16, in acascade arrangement, to achieve a more homogeneous heat dissipation.

FIG. 13 illustrates how the temperature irregularities which limit poweroutput, in particular along the active laser zone 5, can be reduced whenworking with high-performance lasers, in particular. In a separatecontroller, each measuring voltage 14 of corresponding measuring point12 produces its own actuating current 17 for cooling the correspondingheat-dissipation point 15. The dimensional design of the controller isespecially simple, when all reference points 13 and all thermalreference points 16 have the same temperature.

When this temperature control that is selective with regard to locationis used, it is possible, for example, to cool especially hot points moreintensely than less hot points and, in this manner, achieve a uniformtemperature characteristic along the active laser zone 5 of laser chip4.

Using the technology described here, one can easily conceive of otherrefinements or arrangements derived from the particular laser chip andits application area, depending on this requirement.

What is claimed is:
 1. A semiconductor laser comprising: a semiconductorlaser chip; and at least one temperature sensor configured to beintegrated in the semiconductor laser chip for measuring an operatingtemperature, wherein the at least one temperature sensor is secured bywelding directly in the semiconductor laser chip, an energy for thewelding coming from a light source, the light source including at leastone of a ND-glass source, a Nd-YAG source and a source having a similarspatial distribution and similar spectral distribution to a Nd-glasssource or a Nd-YAG source.
 2. The semiconductor laser as recited inclaim 1 wherein prior to the welding each of the at least onetemperature sensor is sealed into an electrically insulating glass. 3.The semiconductor laser as recited in claim 1 wherein each of the atleast one temperature sensor is arranged and secured in a respectivehole, each of the respective hole being formed in the laser chip usinglight-welding.
 4. The semiconductor laser as recited in claim 1 whereinthe at least one temperature sensor is included in the semiconductorlaser chip, wires for measuring an electrical resistance through thesemiconductor laser chip being mounted on the semiconductor laser chip.5. The semiconductor laser as recited in claim 4 wherein the wires formeasuring the electrical resistance through the semiconductor laser chipinclude a pumping current lead wire and an additional wire used as asensor supply lead.
 6. The semiconductor laser as recited in claim 1wherein the at least one temperature sensor includes a thermoelement. 7.The semiconductor laser as recited in claim 1 wherein the at least onetemperature sensor includes a thermoelement having two wires joined bylaser-light welding and secured in a common work step to thesemiconductor laser chip.
 8. The semiconductor laser as recited in claim7 wherein a contact surface of a material of one of the wires isdeposited on the semiconductor laser chip before the two wires arejoined.
 9. A semiconductor laser comprising: at least one firstsemiconductor laser chip; at least one second semiconductor laser chip,the at least one second semiconductor laser chip forming a semiconductorlaser array with the at least one first semiconductor laser chip; atleast one temperature sensor associated with the semiconductor laserchip for measuring an operating temperature, each of the at least onetemperature sensor being one of disposed directly on and integrated in arespective one of the semiconductor laser chip and the at least onesecond semiconductor laser chip for measuring a respective operatingtemperature, an operating temperature of the semiconductor laser arraybeing measurable by measuring the operating temperature of the at leastone first semiconductor laser chip and the at least one secondsemiconductor laser chip, a respective output wavelength of thesemiconductor laser chip and the at least one first semiconductor laserchip and at least one of the second semiconductor laser chip beingadjustable by varying their respective pumping currents.
 10. Thesemiconductor laser as recited in claim 1 wherein each of the at leastone temperature sensor includes a respective thermoelement disposeddirectly on the semiconductor laser chip, each of the thermoelementsbeing operatable in a reversed operation as a respective Peltier elementhaving a current source for adjusting a respective temperature withlocal selectivity.
 11. The semiconductor laser as recited in claim 10wherein the semiconductor laser chip includes an active laser zonehaving at least one measuring point for measuring a wavelength of thesemiconductor laser chip so as to enable an adjusting of the wavelength.12. The semiconductor laser as recited in claim 11 wherein thesemiconductor laser is included in a telecommunications laser and thesemiconductor laser chip includes one measuring point in the activezone.
 13. The semiconductor laser as recited in claim 11 wherein thesemiconductor laser is included in a high-performance laser and thesemiconductor laser chip includes a plurality of measuring points alongthe active laser zone.
 14. The semiconductor laser as recited in claim10 wherein the at least one temperature sensor includes at least twothermoelements operated and configured in a cascade arrangement.
 15. Thesemiconductor laser as recited in claim 1 further comprising: aclosed-loop control circuit including a setter for adjusting theoperating temperature.
 16. The semiconductor laser as recited in claim 1further comprising a respective temperature setter and a respectivetemperature controller associated with each of the at least onetemperature sensor and disposed on the semiconductor laser chip.
 17. Asemiconductor laser comprising: a semiconductor laser chip; and at leastone temperature sensor configured to be disposed directly on thesemiconductor laser chip for measuring an operating temperature, whereinthe at least one temperature sensor is secured by welding directly onthe semiconductor laser chip, an energy for the welding coming from alight source, the light source including at least one of a ND-glasssource, a Nd-YAG source and a source having a similar spatialdistribution and similar spectral distribution to a Nd-glass source or aNd-YAG source.
 18. The semiconductor laser as recited in claim 17wherein prior to the welding each of the at least one temperature sensoris sealed into an electrically insulating glass.
 19. The semiconductorlaser as recited in claim 17 wherein each of the at least onetemperature sensor is arranged and secured in a respective hole, each ofthe respective hole being formed in the laser chip using light-welding.20. The semiconductor laser as recited in claim 17 wherein the at leastone temperature sensor is included in the semiconductor laser chip,wires for measuring an electrical resistance through the semiconductorlaser chip being mounted on the semiconductor laser chip.
 21. Thesemiconductor laser as recite in claim 20 wherein the wires formeasuring the electrical resistance through the semiconductor laser chipinclude a pumping current lead wire and an additional wire used as asensor supply lead.
 22. The semiconductor laser as recited in claim 17wherein the at least one temperature sensor includes a thermoelement.23. The semiconductor laser as recited in claim 17 wherein the at leastone temperature sensor includes a thermoelement having two wires joinedby laser-light welding and secured in a common work step to thesemiconductor laser chip.
 24. The semiconductor laser as recited inclaim 23 wherein a contact surface of a material of one of the wires isdeposited on the semiconductor laser chip before the two wires arejoined.
 25. The semiconductor laser as recited in claim 17 wherein eachof the at least one temperature sensor includes a respectivethermoelement disposed directly on the semiconductor laser chip, each ofthe thermoelements being operatable in a reversed operation as arespective Peltier element having a current source for adjusting arespective temperature with local selectivity.
 26. The semiconductorlaser as recited in claim 10 wherein the semiconductor laser chipincludes an active laser zone having at least one measuring point formeasuring a wavelength of the semiconductor laser chip so as to enablean adjusting of the wavelength.
 27. The semiconductor laser as recitedin claim 11 wherein the semiconductor laser is included in atelecommunications laser and the semiconductor laser chip includes onemeasuring point in the active zone.
 28. The semiconductor laser asrecited in claim 11 wherein the semiconductor laser is included in ahigh-performance laser and the semiconductor laser chip includes aplurality of measuring points along the active laser zone.
 29. Thesemiconductor laser as recited in claim 27 wherein the at least onetemperature sensor includes at least two thermoelements operated andconfigured in a cascade arrangement.
 30. The semiconductor laser asrecited in claim 17 further comprising a respective temperature setterand a respective temperature controller associated with each of the atleast one temperature sensor and disposed on the semiconductor laserchip.
 31. The semiconductor laser as recited in claim 9 wherein the atleast one temperature sensor is disposed directly on the semiconductorlaser chip for measuring an operating temperature.
 32. The semiconductorlaser as recited in claim 9 wherein the at least one temperature sensoris integrated in the semiconductor laser chip for measuring an operatingtemperature.
 33. The semiconductor laser as recited in claim 15 whereinthe at least one temperature sensor is disposed directly on thesemiconductor laser chip for measuring an operating temperature.
 34. Thesemiconductor laser as recited in claim 15 wherein the at least onetemperature sensor is integrated in the semiconductor laser chip formeasuring an operating temperature.